1. Field of the Invention
The present invention relates to bumped wafers for chip devices, and more particularly, to a new passivation scheme for bumped wafers.
2. Description of the Prior Art
The primary component of today""s chip devices is at least one die. The die generally consists of a wafer that has been passivated. The passivation process for today""s wafers generally include masking steps and an expensive planarization process.
Because of the masking layers, the metal layer(s) is generally thinner. In a MOSFET device, a passivation layer is placed over the metal layer to protect it. This can result in an increased resistance from the drain to the source region when the chip device is on. Conventional passivation methods include using silicon nitride as a passivation layer. However, as noted, such use can result in extra steps and increased processing expanse in wafer manufacture.
The present invention provides a bumped wafer that includes two titanium layers sputtered alternatingly with two copper layers over a non-passivated die. Presently, the bumped wafer includes under bump material under the solder bumps contained thereon.
The present invention also provides a method of making the bumped wafer. The method includes providing a non-passivated die and alternatingly sputtering titanium, copper and titanium and copper thereon. A photo process is then performed and an isolation etch is performed in order to remove the top copper layer, the second titanium layer and the bottom copper layer at the isolation location. A photo process is then once again performed in order to create an area for the under bump material that is under the solder bumps. The top layers of copper and titanium are then etched away at the locations on the wafer where the solder bumps will be placed. The under bump material is then deposited thereon and the solder is placed over the under bump material. The photo resist material is then stripped away and the bottom layer of titanium is etched at the isolation locations. The remaining top layer of the copper is then etched away and the solder is reflowed in order to shape the solder into a substantially xe2x80x9cballxe2x80x9d shape.
Thus, the present invention provides a bumped wafer and a method of manufacture thereof wherein the bumped wafer includes a titanium passivation layer. The titanium tends to passive itself and adhere well to copper as well as aluminum thereby forming a good interlayer. Solder does not wet to the titanium layer, thus providing for defined solderable surfaces in a wafer. Additionally, the copper interlayers (over the aluminum) offer a solderable surface that can be plated and/or sputtered.
Other features and advantages of the present invention will be understood upon reading and understanding the detailed description of the preferred exemplary embodiments, found hereinbelow in conjunction with reference to the drawings in which like numerals represent like elements.